JP4885954B2 - Electroless pure palladium plating solution - Google Patents

Description

  The present invention relates to an electroless pure palladium plating solution, and more particularly, to an electroless pure palladium plating solution that can form a pure palladium plating film with little variation in plating film.

In electronic parts that require high density and high reliability, surface treatment of electronic parts that require wire bonding mounting or solder mounting should be treated with a noble metal that has corrosion resistance and excellent electrical characteristics. Is effective, especially gold plating film.
However, since gold is a rare value material, its price has risen remarkably due to market prices, and technological development of alternative metals has attracted attention.
In particular, since palladium is less expensive than gold bullion, it has been in the spotlight as an alternative metal for reducing the thickness of the gold plating film.
However, in recent years, not only the price but also the characteristics, stability, and reliability of the palladium plating film have been attracting attention in highly reliable electronic parts in which the density of wiring is accelerated.

  Conventionally, as an electroless palladium plating solution used in industrial applications, for example, as described in Patent Document 1, it is composed of a water-soluble palladium salt, ethylenediaminetetraacetic acid, ethylenediamine, and sodium hypophosphite. Known electroless palladium plating solutions are known.

  Also, electroless palladium containing at least one of a palladium compound, ammonia and an amine compound, an organic compound containing divalent sulfur, and at least one of a hypophosphite compound and a borohydride compound as essential components Plating solutions are also known. (For example, refer to Patent Document 2). A palladium-phosphorus alloy plating film is obtained from these electroless palladium plating solutions.

  On the other hand, an electroless palladium plating solution comprising at least one selected from a palladium compound, ammonia and an amine compound, at least one selected from formic acid, sodium formate and potassium formate is also known. (For example, refer to Patent Document 3).

The electroless palladium plating solution of Patent Document 1 described above has not only poor storage stability, but also has a defect that it decomposes in a short time in an industrial mass production line and the life of the plating solution is short. Moreover, since all the plating films obtained from this plating solution have many cracks, and the wire bonding property and solderability are not good, there is a difficulty in application to electronic parts. In addition, the electroless palladium plating solution disclosed in Patent Document 2 includes palladium film characteristics before and after the heat resistance test because phosphorus and boron derived from hypophosphorous acid compounds and boron compounds as reducing components are mixed in the plating film. There was a defect that changed significantly.
Furthermore, the electroless palladium plating solution of Patent Document 3 has excellent storage stability and stable palladium film characteristics before and after the heat resistance test, but in the industrial mass production line, with the prolonged use of the plating solution, This presents a technical problem that the film thickness variation becomes large and the film thickness control is difficult.

Japanese Examined Patent Publication No. 46-26764 Japanese Patent Laid-Open No. 62-124280 Japanese Patent No. 3035763

  An object of the present invention is to provide an electroless palladium plating solution that can be practically used in an industrial mass production line and can form a stable pure palladium plating film on the wiring of a highly reliable fine wiring electronic component. To do.

That is, this invention consists of following (1)-(5).
(1) (a) 0.001 to 0.5 mol / l of a water-soluble palladium compound, and (b) at least two or more selected from aliphatic carboxylic acids and water-soluble salts thereof from 0.005 to 10 mol / l. In electroless pure palladium plating solution containing,
(C) further comprises the electroless pure palladium plating solution as an essential component of formic acid or formate salt
(D) is at said aliphatic carboxylic acid is an aliphatic monocarboxylic acid, an aliphatic polycarboxylic acid, at least one or more selected from the group of contact and aliphatic hydroxycarboxylic acid,
(E) phosphoric acid and / or phosphate 0.005 to 10 mol / l, and (f) sulfuric acid and / or sulfate 0.005 to 10 mol / l,
(G) An electroless pure palladium plating solution characterized by further containing ammonia and / or an amine compound .
(2) The electroless pure palladium plating solution according to claim 1, wherein the water-soluble palladium compound is palladium chloride.
(3) The electroless pure palladium plating solution according to any one of claims 1 to 2, wherein the amine compound is ethylenediamine.
(4) The electroless pure palladium plating solution according to any one of claims 1 to 3, wherein the aliphatic oxycarboxylic acid is malic acid, citric acid, tartaric acid, gluconic acid, glycolic acid and lactic acid.
(5) The electroless pure palladium plating solution according to any one of claims 1 to 4, wherein the aliphatic polycarboxylic acid is oxalic acid, malonic acid, maleic acid, succinic acid, and glutaric acid.

Examples of the water-soluble palladium compound used in the present invention include palladium chloride, sodium palladium chloride, potassium potassium chloride, palladium ammonium chloride, palladium sulfate and palladium acetate.
The palladium concentration in the electroless palladium plating solution is preferably in the range of 0.0001 to 0.5 mol / l. A concentration of 0.0001 mol / l or less is not preferable because the plating film deposition rate is slow, and a concentration of 0.5 mol / l or more is not practical because the deposition rate is not improved further.

In the plating solution of the present invention, at least one of ammonia and / or an amine compound is used in order to maintain the stability of the solution.
Ammonia and / or amine compounds form a complex with the palladium compound in the plating solution to stably hold these components in the solution, and contribute to stabilization of the solution. The concentration of the ammonia and / or amine compound is 0.0005 to 8 mol / l, preferably 0.01 to 5 mol / l. When ammonia is used alone, the concentration is preferably 0.05 to 1 mol / l or more in order to improve the stability of the plating solution.
The higher the concentration of ammonia and / or amine compound, the better the stability of the plating solution. However, when the concentration exceeds the above concentration, it is uneconomical, especially when ammonia is used, because the working environment becomes worse due to odors and the like. It is not preferable. On the other hand, when the concentration is lower than the above-mentioned concentration, it is not preferable because the stability of the plating solution is lowered and the palladium complex is easily separated.

  Examples of the amine compound used in the present invention include monoamines such as methylamine, ethylamine, propylamine, trimethylamine, and dimethylethylamine, diamines such as methylenediamine, ethylenediamine, tetramethylenediamine, and hexamethylenediamine, diethylenetriamine, and pentaethylenehexamine. Examples of such polyamines and other amines include ethylenediaminetetraacetic acid and its sodium salt, potassium salt, ammonium salt, glycine, and iminodinacetic acid.

  In the present invention, at least one of the above ammonia and / or amine compound may be used. However, when ammonia is used alone, the time until the plating film starts to be deposited may be long. In this case, the time can be shortened by adding an amine compound as an oxidizing agent. In the plating solution to which the amine compound is added, the appearance of the plating film when the plating film is thickened is particularly good.

Aliphatic carboxylic acids and their water salts include aliphatic monocarboxylic acids such as acetic acid , propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, maleic acid, succinic acid, glutaric acid, etc. Aliphatic carboxylic acids such as aliphatic polycarboxylic acid, malic acid, citric acid, gluconic acid, tartaric acid, glycolic acid and lactic acid, and sodium salts, potassium salts and ammonium salts of these aliphatic carboxylic acids.
The plating solution of the present invention contains a formic acid or formic acid salt as essential components, further aliphatic monocarboxylic acids, aliphatic polycarboxylic acids, one or more aliphatic carboxylic acids and their water selected from aliphatic oxycarboxylic acid Contains salt.
The use concentration of the aliphatic carboxylic acid in the plating solution is 0.005 to 5 mol / l, preferably 0.01 to 1 mol / l.
When the concentration is 0.005 mol / l or less, the plating film is not sufficiently formed, and when the concentration is 5 mol / l or more, the deposition rate is in an equilibrium state and does not improve any more, so it is not practical.

  In the present invention, the pH of the plating solution is preferably pH 3 to 10, particularly pH 5 to 8. If the pH is too low, the stability of the plating bath decreases, and if the pH is too high, cracks are likely to occur in the plating film, which is not preferable.

In the present invention, phosphoric acid and / or phosphate and sulfuric acid and / or sulfate are used in combination in order to improve the pH buffering action.
Examples of phosphoric acid and phosphate include orthophosphoric acid and salts thereof.
Examples of the sulfate include sodium sulfate, potassium sulfate, ammonium sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, and ammonium hydrogen sulfate.
The concentration of the phosphoric acid and / or phosphate and sulfuric acid and / or sulfate is preferably 0.005 to 10 mol / l.

The plating solution of the present invention can be plated in a wide temperature range of 20 to 90 ° C., and a smooth and glossy good plating film can be obtained particularly at a solution temperature of 40 to 80 ° C. Further, the higher the liquid temperature, the higher the deposition rate of the plating film, and the deposition rate can be arbitrarily set by appropriately setting the temperature within the above temperature range.
Furthermore, in the plating solution of the present invention, the deposition rate of the plating film depends on the palladium concentration in addition to the temperature of the plating solution. Therefore, the deposition rate of the plating film can be adjusted by appropriately setting the palladium concentration. Therefore, the film thickness of the plating film can be easily controlled.

  In order to form a plating film with the plating solution of the present invention, a substrate having a catalytic property for reduction deposition of a palladium film may be immersed in the plating solution within the above temperature range. Examples of the catalytic substrate include iron, nickel, cobalt, gold, silver, copper, platinum, palladium, and alloys thereof.

Moreover, even if it is a non-catalytic substrate such as resin, glass, ceramics, etc., it is immersed in the plating solution in the same manner as the above method by imparting catalytic properties by a known method such as a sensitizing-activator method. Thus, a plating film can be formed.
The deposition of the palladium film by the electroless pure palladium plating solution of the present invention proceeds in an autocatalytic manner. Therefore, a film having a small porosity, a dense film, and excellent adhesion can be obtained.

The electroless palladium plating solution of the present invention has very good storage stability and can be deposited at a low temperature, so that the workability is good and the working environment is also good. Further, since the deposition rate depends on the palladium concentration and the solution temperature, the plating film thickness can be easily controlled.
And high purity palladium with favorable catalytic activity is obtained, without mixing phosphorus and a boron into a plating film.
The plating film obtained by the plating solution of the present invention has very few cracks and is excellent in solderability and wire bonding properties. Since the plating solution of the present invention has excellent characteristics as described above, it is of great practical value as a plating material for various electronic components that require high reliability.

    EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, unless the summary is exceeded.

Composition of plating solution Palladium chloride 0.05 mol / l
Ethylenediamine 0.03 mol / l
Malic acid 0.05 mol / l
Citric acid 0.05 mol / l
Sodium formate 0.30 mol / l
Disodium hydrogen phosphate 0.1 mol / l
Sodium sulfate 0.1 mol / l
Sodium hydroxide pH 6.0 when combined with the above ingredients
Added.

Composition of plating solution Palladium chloride 0.05 mol / l
Ethylenediamine 0.03 mol / l
Maleic acid 0.05 mol / l
Citric acid 0.05 mol / l
Sodium formate 0.30 mol / l
Disodium hydrogen phosphate 0.1 mol / l
Sodium sulfate 0.1 mol / l
Sodium hydroxide pH 6.0 when combined with the above ingredients
Added.
{Comparative Example 1}

Composition of plating solution Palladium chloride 0.05 mol / l
Ethylenediamine 0.03 mol / l
Malic acid 0.05 mol / l
Sodium formate 0.30 mol / l
Sodium hydroxide pH 6.0 when combined with the above ingredients
Added.
{Comparative Example 2}

Composition of plating solution Palladium chloride 0.05 mol / l
Ethylenediamine 0.03 mol / l
Malic acid 0.05 mol / l
Disodium hydrogen phosphate 0.10 mol / l
Sodium formate 0.30 mol / l
Sodium hydroxide pH 6.0 when combined with the above ingredients
Added.

A printed circuit board having an independent ball grid array type copper electrode having a diameter of 0.5 mm was subjected to a conventional pretreatment, followed by a commercially available electroless nickel plating (phosphorus content: 8%). A nickel plating film was formed. After washing with running water for 1 minute, plating was carried out using the electroless pure palladium plating solution prepared in the above-mentioned Examples and Comparative Examples, with a plating temperature of 70 ° C. and a plating time of 5 minutes.
Subsequently, the thickness of the palladium film was measured, and the variation in the plating rate and the film thickness was examined. The thickness of the plating film was measured with a fluorescent X-ray microfilm thickness meter.
The results are shown in Table 1.

In Table 1, the unit is μm / 5 minutes.
A numerical value shows an average value, and a numerical value in parentheses is a variation value of the film thickness.

As described above, the deposition rate of the electroless pure palladium plating and the variation in the thickness of the palladium film were measured. As a result, in the case of the comparative example, the variation value of the film thickness increased with the passage of time of the building bath, and the maximum was 0. .33 μm.
On the other hand, in the case of the example according to the present invention, the deposition rate and the stability of the plating solution are good even when the time after the bathing has elapsed, and the variation of the palladium plating film thickness is half that of the comparative example. confirmed. Moreover, when the soldering property and wire bonding property were evaluated about the fine wiring board used for the test, the favorable result was shown.

Since the present invention was able to form a stable pure palladium plating film on the wiring of highly reliable fine wiring electronic parts, there was little variation in the plating film, and it was possible to form a pure palladium plating film, especially electroless pure palladium plating. Highly applicable in the liquid industry.

Claims (5)

(A) 0.001 to 0.5 mol / l of a water-soluble palladium compound, and (b) at least two or more selected from aliphatic carboxylic acids and water-soluble salts thereof 0.005
In an electroless pure palladium plating solution containing 10 mol / l,
(C) Further, the electroless pure palladium plating solution contains formic acid or formate as an essential component.
Including
(D) the aliphatic carboxylic acid is an aliphatic monocarboxylic acid, an aliphatic polycarboxylic acid, and
And at least one selected from the group of aliphatic oxycarboxylic acids,
(E) phosphoric acid and / or phosphate 0.005 to 10 mol / l, and
(F) containing sulfuric acid and / or sulfate 0.005 to 10 mol / l,
(G) Electroless pure liquid further comprising ammonia and / or an amine compound.
Radium plating solution.     The electroless pure palladium plating solution according to claim 1, wherein the water-soluble palladium compound is palladium chloride.     The electroless pure palladium plating solution according to claim 1, wherein the amine compound is ethylenediamine.     The electroless pure palladium plating solution according to any one of claims 1 to 3, wherein the aliphatic oxycarboxylic acid is malic acid, citric acid, tartaric acid, gluconic acid, glycolic acid and lactic acid.     The electroless pure palladium plating solution according to any one of claims 1 to 4, wherein the aliphatic polycarboxylic acid is oxalic acid, malonic acid, maleic acid, succinic acid, and glutaric acid.